With the development of high-speed network infrastructure and with the development of large capacity recording media, the absolute quantity of video data that can be handled at a time by the user or by user video equipment has markedly increased. With this trend, various functions that are achieved using a plurality of sets of video data and high-performance applications based on such functions have been emerging. As one of such functions, there is a function called “picture in picture”.
“Picture in picture” is a function for displaying two videos at the same time by superimposing a small child frame over the screen (parent frame). This function is used for, for example “multi-angle representation” for displaying, in the child frame, a video taken from a different angle of view from that of the video for the parent frame or for “commentary display” for displaying additional information in a commentary style as to the video of the parent frame (for example, displaying in the child frame a director's commentary video or the like recorded with untold stories during shooting the movie).
Picture in picture is realized for example by decoding two sets of video data over two different layers and superimposing these decoded videos, as shown in FIG. 17. In this case, the video for the child frame is adjusted in its display size and displayed position in order to be laid over the parent frame. Also, the child frame at the time of picture in picture may have a video of an arbitrary shape, other than the rectangular video shown in FIG. 17. The picture-in-picture function and the method of realizing it are described in for example patent document 1.
Patent document 1:
    Japanese Patent Application Laid-open 2005-123775